Dana Reeve, the heroic actress-singer widow of “Superman” star Christopher Reeve, has lost her fight with cancer at the age of 44.

She died late Monday night at Memorial Sloan-Kettering, just six months after her illness was diagnosed, and 17 months after the death of her husband.

Her death was the latest in the chilling string of tragedies to strike people associated with Superman – starting with the mysterious 1959 shooting death of George Reeves, the actor who played the Man of Steel in the classic TV series.

Just as her husband showed grace, humor and determination in his struggle to overcome his paralysis, Dana Reeve pressed on with courage and optimism, intent on beating her inoperable lung cancer.

“I had a great model. I was married to a man who never gave up,” she told a crowd at a Christopher Reeve Foundation fund-raiser last November, three months after her grim diagnosis, wearing a wig to cover her chemo-induced hair loss.

“I’m beating the odds and defying every statistic the doctors can throw at me,” she vowed as she reported that her tumor was “shrinking and shrinking and shrinking.”

Ever optimistic, she spoke of the future in a TV interview the next day: of helping disabled victims of Hurricane Katrina through the Christopher Reeve Foundation; of doing charity work for lung cancer “if I have the energy . . . I think it’s sort of an obligation;” and of her “plan to sing again. I have enough lung capacity.”

She did sing again – she appeared at Madison Square Garden in mid-January, belting out Carole King’s “Now and Forever” at a New York Ranger ceremony honoring hockey great Mark Messier.

Kathie Lee Gifford, who interviewed Dana that evening, recalled that she appeared thin but was full of optimism and said her tumor was still shrinking.

Then, last month, she took a turn for the worse. The tumor started growing again and the cancer had spread.

She was hospitalized two weeks ago, but “right up [until] the end . . . Dana was convinced she was going to overcome this,” said Kate Michelman, a member of the foundation’s board.

Dana lost her last fight late Monday night with just a few friends at her bedside.

She had been limiting her visitors to a small group of family members and close friends, including comedian Robin Williams and his wife, Marsha.

Her death came after a series of personal tragedies that started with the paralysis of her actor husband in a horse-riding accident in May 1995, after just three years of marriage and the birth of their son, Will.

She spent the next nine years as her quadriplegic husband’s loving caregiver – as well as a fellow fund-raiser and crusader for spinal-cord and stem-cell research.

He died in October 2004, at the age of 52.

Just months after that, as Dana was still reeling, her mother died after undergoing surgery for ovarian cancer.

In August, while trying to deal with the twin losses and helping her son, Will, cope with the crippling blows, doctors told her she had lung cancer – even though she was not a smoker.

She broke the news to her pianist, Charlie Alterman, telling him, “Well, I guess I know what my cough was,” he recalled yesterday.

“That was the way she was, always cracking jokes,” he said.

Longtime friend Bonnie Monte, artistic director of the Shakespeare Theater of New Jersey, said, “There was still so much she wanted to do – but she ran out of time.”

Monte witnessed romance blossom between Dana Morosini of Scarsdale and Hollywood’s Christopher Reeve in 1987, when they met at the Williamstown Theater Festival in Williamstown, Mass., where he was acting and she was singing in a late-night cabaret.

“It was intense attraction at first sight . . . which developed very quickly into love,” the “Superman” actor told an interviewer.

Five years later, in 1992, they married and Will was born.

Then, in 1995, he had his horse accident.

Before he underwent surgery to have his skull reattached to his spinal column, he told Dana it might be better for all involved if he just ended it all.

She answered that she married him for the long haul, telling him, “You’re still you, and I love you.”

He used a variation of her words, “Still Me,” as the title of his 1998 memoir.

She took breaks from her caregiving to resume her career, singing and appearing on “Law & Order,” “Oz” and other TV series.

She was in California, performing in the Broadway-bound play “Brooklyn Boy,” when Reeve slipped into a coma.

She rushed home to Westchester to be with him, and dropped out of the play after his death.

She continued raising Will at their home in Pound Ridge, with help from her extended family – including her stepchildren, Alexandra, 22, and Matthew, 26, Reeve’s children with Gae Exton.

A month before her diagnosis, she talked of resuming her career.

“I definitely will be getting back to acting . . . I am an actress and I do have to make a living,” she told a reporter.

Among those mourning her loss yesterday was actor John Lithgow.

“Dana endured terrible things, but never did I hear her speak a self-pitying word,” he said.

“She was a woman with genius for compassion. She gave strength not just to Chris, but to everyone who knew them both.”

Actress Susan Sarandon recalled Dana’s “fierce grace.”

“Under pressure, she embraced her personal struggles with dignity and humor . . . She filled her life with love as clear and unflinching as her beautiful voice,” Sarandon said.

In addition to her son and stepchildren, Dana is survived by her father, Dr. Charles Morosini, and her sisters, Deborah Morosini and Adrienne Morosini Heilman.

No funeral arrangements have been announced.

The family has asked that donations be made in Dana Reeve’s memory to the Christopher Reeve Foundation in Short Hills, N.J.